In the process of electrostatographic reproduction, a light image of an original to be copied or printed is typically recorded in the form of a latent electrostatic image upon a photosensitive member, with a subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support medium, such as a sheet of plain paper. To render this toner image permanent, the image must be “fixed” or “fused” to the paper, generally by the application of heat and pressure.
With the advent of high speed xerography reproduction machines wherein copiers or printers can produce at a rate in excess of three thousand copies per hour, the need for sheet handling system to, for example, feed paper or other media through each process station in a rapid succession in a reliable and dependable manner in order to utilize the full capabilities of the reproduction machine. These sheet handling systems must operate flawlessly to virtually eliminate risk of damaging the recording sheets and generate minimum machine shutdowns due to misfeeds or multifeeds. It is in the initial separation of the individual sheets from the media stack where the greatest number of problems occur which, in some cases, can be due to up curl and down curl in sheets which generally occur randomly in the document stack.
Applicant has found that previous approaches incorporated a venturi fluffer (U.S. Pat. No. 6,264,188 to Taylor et al.) to break apart the sheets on the stack. That patent discloses a venturi fluffer utilizing internal and external flaps in order to maintain a relatively constant throat cross section and pressure to achieve sheet separation. The venturi fluffer provided satisfactory performance in uncoated papers up to 200 gsm, slightly lower with coated stocks due to an observed lack of sufficient air pressure to break up the sheet pairs inherent in coated stocks, even with heat. The venturi fluffer provided a wide throat cross section that delivered sufficient air volume to maintain sheet separation, once achieved, but at an insufficient pressure necessary to break up sheet pairings observed during testing. Various combinations of fluffer pressure settings and configurations provided little relief across the wide range of media types prescribed.
Other high pressure fluffing systems use multiple blower pressure settings to provide the correct air flow rate and pressure into the side of a stack. All of the systems have pressure losses due to air flowing above the stack.